On Monday, 27 August 2012 at 23:09:13 UTC, F i L wrote:
foobar wrote:
FiL's scheme looks backwards to me. One of the main drawbacks
of factories is the fact that they have non-standard names.
Given a class Foo, How would I know to call a factory newFoo?
Well you'd know to call constructor functions because their
name implies they construct an object: new(), load(), from(T),
etc.. I _hate_ global functions like in my newFoo() example. I
was simply using it as an example of where factories hide
information about what's being returned in today's code.
Constructor functions in my proposal must always be attached to
a type, and can't be global, but their names are arbitrary
(which is good for overload distinction, like I've explained
before).
class LimitedAccount : Account {
// "regular allocation" - on GC heap
private Account new(Person p) {
return GC.allocate!LimitedAccount(P);
}
// init
this(Person p) {...}
...more code...
}
class Bank {
Account new(Person p, AccountType t) {
switch(t) {
case AccountType.LIMITED: return LimitedAccount.new(p);
... more cases...
}
}
}
// usage:
Account acc = Bank.new(PoorShmoe, AccountType.LIMITED);
This is pretty much exactly what I am advocating except I think
the allocator and c-tor can be combined (with a attribute
override), since the allocator is implicit half the time. I
gave an example in my original post:
class Foo {
this new() {
// Implicitly allocates Foo.
}
this new() @noalloc {
// Allocation must be explicit
// but must return type Foo.
}
static auto new() {
// Regular factory function.
// Allocate and return at will.
}
}
Not at all.
Your scheme requires new to return typeof(this) whereas in mine
Bank.new() returns an Account instance.
Also, allocation needs to be explicit in order to be useful.
Most importantly, the naming scheme you suggest breaks generic
code. I _DON'T_ want to choose between "new/from/load/etc.." when
I create an object. I just want to create an object, period.
There are whole frameworks of DI just to "fix" this problem of
new and factories.
Please google for "java new considered harmful" to read more
about this.
